(1) Field of the Invention
The present invention relates to the structure of a nuclear magnetic resonance probe that is included in a nuclear magnetic resonance (NMR) apparatus composed at least of a superconducting magnet which is a means for applying a static magnetic field to a specimen and a low-temperature probe having a probe coil formed in the distal part thereof, and that has the probe coil thereof realized with superconducting thin films formed on respective substrates.
(2) Description of the Related Art
The structure of a nuclear magnetic resonance probe coil realized with superconducting thin films has been discussed in, for example, “Review of Scientific Instruments” (Vol. 69, 1998, pp. 2708-2712) or the specification of U.S. Pat. No. 6,556,013. The documents describe the structure of a probe coil realized with superconducting thin films. The probe coil is realized by forming the superconducting thin films on respective substrates. For example, “IEEE Transactions on Biomedical Engineering” (Vol. 43, No. 12, 1996, pp. 1197-1199) has disclosed a superconducting thin-film ring formed on a substrate to include an interdigital capacitor.
The application of a large homogeneous static magnetic field to a specimen or the employment of a high-sensitivity probe coil is effective in realizing a high-resolution high-sensitivity nuclear magnetic resonance apparatus. For induction of a homogenous strong magnetic field, the diameter of a probe coil made of a wire material that generates a magnetic field should be decreased, and a space occupied by the probe coil should be limited. The probe coil forms a resonant circuit. For realization of a high-sensitivity probe coil, the quality (Q) factor of the probe coil should be improved. For a high Q factor, the resistance offered by the probe coil realizing the resonant circuit should be minimized.
Attempts to manufacture a probe coil using superconducting thin films have been discussed in the above documents. The DC resistivity of a superconductor is zero, and the resistance offered thereby at a radiofrequency is small. Therefore, the superconductor is useful as a component of the probe coil.
The adoption of a probe coil realized with superconducting thin films is helpful in attaining a high Q factor. However, a superconductor is perfectly diamagnetic by nature and has a large magnetic susceptibility of −¼π. Therefore, the probe coil should be designed not to disorder a static magnetic field but to maintain the homogeneity of the static magnetic field.
“Review of Scientific Instruments” (Vol. 69, 1998, pp. 2708-2712) has introduced an example of a probe coil to which a static magnetic field is horizontally applied and which has superconducting thin-film rings formed on the face and back of a substrate. The normal to the surface of the substrate is extended vertically, and a specimen is put into the superconducting thin-film rings. Since the normal to the surface of the substrate and the direction of the static magnetic field are orthogonal to each other, a volume of the static magnetic field interacting with a superconductor is limited. Therefore, the disorder of the static magnetic field caused by the superconductor having a large magnetic susceptibility is limited. Since the specimen is put into the superconducting thin-film rings, a magnetic moment exhibited by the specimen can be highly efficiently measured. In other words, since a fill factor by which the specimen occupies the space where the probe coil can measure the magnetic moment is high, the foregoing structure is preferable for realizing a high-sensitivity probe coil. However, “Review of Scientific Instruments” (Vol. 69, 1998, pp. 2708-2712) is concerned with the probe coil including only one coil but has not taken account of a preferable structure including multiple coils needed to measure many nuclear species. Moreover, although the probe coil is magnetically coupled to a means for transmitting a signal, no consideration is taken into a method of strengthening the coupling and improving the signal intensity.
U.S. Pat. No. 6,556,013 describes an example of a probe coil to which a static magnetic field is applied horizontally and which has patterns or superconducting thin films formed on the surfaces of respective substrates. U.S. Pat. No. 6,556,013 discusses a structure designed to include multiple coils for the purpose of measuring many nuclear species. However, the direction of a static magnetic field is vertical. No consideration is taken into a structure including multiple coils and being adapted to a nuclear magnetic resonance apparatus in which the direction of a static magnetic field is horizontal.